Control for harmonic suppressor



April 5, 1960 E. B. HILKER 2,931,968

CONTROL FOR HARMONIC SUPPRESSOR Filed Sept. 30, 1957 3 Sheets-Sheet l April 5, 1960 E. B. HILKER 2,931,968

CONTROL FOR HARMONIO sUPPREssOR Filed Sept. SO, 1957 3 Sheets-Sheet 2 /fvra can/fra Www/V65 myn/vae 96 April 5, 1960 E. B. HILKER CONTROL FOR HARMONIO sUPPREssOR 3 Sheets-Sheet 5 Filed Sept. 30, 1957 YC Y@ *Ms FIG] lllllalilb uUIIHl:

774 tra ys United States Patent() 2,931,968 CoNTRoL Fon HARMoNIc sUPPREssoR Erwin B. Hilker, deceased, late of St. Louis, Mo., by

Anuamary Hilker, admnistratrix, St. Louis, Mo., assignor to Wagner Electric Corporation, St. Louis, Mo., a corporation of Delaware Application September 30, 1957, Serial No. 687,084 24 Claims. (Cl. 323-66) The present invention relates generally to the voltage control art and more particularly to novel automatic control means in combination with a harmonic and -*phase shift suppressor of the type shown and described in copending application, Serial No. 680,342, liled August 26, 1957, for use with a voltage control device of the type shown and described in copending application, Serial No. 429,465, filed May 13, 1954, and J. S. Malsbary Patent No. 2,892,146, issued June 23, 1959.

A voltage control device of the type disclosed in the aforementioned applications includes means for providing a variable compensating or adjusting voltage which is superposed on, or injected into, either the input or output voltage of a transformer so as to maintain the output voltage of the transformer at substantially the desired value regardless of change in the supply voltage withinl predetermined limits. The compensating voltage is developed in a bridge circuit, as for example, a Wheatstone type bridge circuit of four saturable core reactors whose impedances. are made responsive to selected external conditions such as voltage or current; the magnitude and phase of the compensating voltage being determined by the relative impedance values of the arms of the bridge.

Although the aforementioned control device has operated very satisfactorily, it has been-found that under certain operating conditions the output voltage contains so-called higher harmonics which may interfere with telephonie,communications; also,`there is at times an undesirable phase shift between the supply and output voltages.

The harmonic and phase shift suppressor, disclosed in the abovementioned application, Serial No. 680,342 substantially eliminates the harmonic components otherwise present in the output voltage, and maintains the phase shift between supply voltage and output voltage small and substantially constant. In the last mentioned application, the suppressor means comprises a variable impedance device (shownin the preferred embodiment as a saturable core reactor) connected across the bridge circuit in which the compensating voltage is developed; with means for manually controlling the impedance of the reactor.

The present invention concerns a phase shift and harmonic vsuppressor and means for automatically controlling the suppressor in response to preselected conditions. Briey, the present invention comprises a variable impedance device connected across the bridge circuit in which the variable voltage is developed, and means for automatically varying the impedance of the device in response to variations in an electrical condition to be controlled whereby the impedance of the device is relatively low when the electrical condition is at a predetermined desired value, and relatively high when the electrical condition varies from the desired value.

It is an object of the present invention to provide novel control means for automatically controlling a harmonic and phase shift suppressor of the aforementioned 2,931,968 Patented Apr. 5, 1960 type. More particularly, it is an object to provide such control means which are responsive to the varations in selected electrical conditions in the circuit, as for example, voltage and current values.

Another object is to provide an electric control system of the aforementioned type wherein the output voltage of the system is automatically maintained substantially free of harmonic components.

Another object is to provide an electric control system of the aforementioned type wherein the phase shift between the supply voltage and output voltage of the system is automatically maintained small and substantially constant.

Another object is to provide a novel fully automatic voltage control system having a controlled saturable core reactor bridge providing a compensating voltage for maintaining an electrical condition of the system substantially constant, wherein the phase shift between the supply voltage and output voltage of the system is maintained small and the harmonic components otherwise present in the output voltage are greatly reduced.

Further objects and advantages of the present inven-v tion will be apparent from the detailed description, reference being had to the accompanying drawings wherein preferred embodiments of the present invention are shown.

In the drawings:

Fig. 1 is a schematic diagram of a preferred embodiment of the present invention,

Fig. 2 is a graph of the characteristic curve of the volt- Fig. 7 is a partial schematic diagram illustrating a modified embodiment of the suppressor control.

Referring to the drawings and particularly to Fig. l, there is shown for illustration an automatic voltage control device 10 which is of the type shown and described in copending application, Serial No. 497,978. Shown in combination with the control device is a harmonic and phase shift suppressor 12, and suppressor control means 14 for automatically controlling the impedance of the suppressor 12. The automatic voltage control circuit 10 includes a power transformer 16, a compensating voltage device 18, and control means 20 for automatically controlling the operation of the device 18 to maintain the output voltage V2 of the transformer 16 substantially constant regardless of changes in supply voltage V1 within predetermined limits. It will be assumed for purposes of illustration only, that the output voltage V2 is held substantially constant while the supply voltage V1 may vary within the range of of the normal or desired value.

The transformer 16 includes a primary winding 22 which is connected through the compensating voltage device 13 and power lines 23 and 24 to an A.C. voltage supply source indicated at 25, a secondary winding 26 which is connected to conductors 27 and 28 for supplying power to a load29, and a corrector winding 30 which will be considered hereinafter.

The compensating voltage device 18 includes a Wheatstone type bridge circuit 32 shown as having four saturable core reactors 34, 36, 38 and 40 connected together to form the four impedance arms of the bridge. Each reactor has a saturable magnetic core on which is positioned an alternating current reactance winding, and a direct current control winding for controlling the magnetic saturation of the core and the impedance of the A.C. winding. The windings of each reactor are identified in the drawing by corresponding like numerals with the letters AC or DC added thereto.

The windings 34AC and SGAC are connected together at a corner 4Z, the windings SGAC and 38AC are connected together at a corner 44, the windings 38AC and 40AC are connected together at a corner 46, and the windings 40AC and ,MAC are connected together at a corner 48. o

The control windings MDC and 38DC of the bridge circuit 32 are connected in series circuit relation, anda signal applied vto this pair of series connected control windings will determine the impedance of the diametrically opposite reactance windings 34AC and 38AC. The

control windings 36DC-and MDC are also connected in series circuit relation, and a signal applied to this pair of control windings will determine the impedance ofthe other diametrically opposite reactance windings 36AC and 40AC.

and a common D.C. control winding. ffEach of the outer legs would be provided with an A.C; winding while the center leg is provided with the common D.C. winding. In such'a case, the bridge circuit contains two sets of s aturable core reactors with each set combined into a twin reactor. v

A conductor 49 connects one end of the primary winding 22 to the corner 48 of the bridge circuit, and the diametrically opposite corner 44 of the bridge. circuit is connected to the power line 23. The other diametrically opposite corners 42 and 46 are connected across the corrector winding 30 through theconductors 50 and 51', respectively. l The corrector winding Sti provides a voltage which is impressed across the corners 42 and 46 ofthe bridge circuit so as to provide a compensating or'adjusting voltage en 48 of the bridge. It will be assumed for purpose of discussion, that the number of turns of the correctorwinding is of the number of turns of the primary winding 22 so that the voltage across the corrector winding is 10% of the induced voltage, thus permitting compensation for approximately a 16% change in the supply voltage. The compensating voltage e is effectively in'series with the primary winding voltage E, and, depending upon the `balance conditions or relative impedances of the two pairs of diametrically opposite reactors of the bridge circuit, the voltage e is either substantially ineffectual,Y

which appears across the other corners 44 and 'assises aiding, or opposing the supply voltageVl, to thereby Vaffect the induced voltage E in such manner as to mainterminals 54 shown connected across the output circuit of the transformer 16 through conductors 55 and S6, and

a pairv of detector output terminals 58 connected to supply control signals to a pair of amplifiers eti and 62. The output of these amplifiers supply the current to the DC. control windings of the bridge. Y

The amplifiers 60 and 62 shownA in the drawing are` self-saturating magnetic amplifiers of the well known type. The amplifier 60 includes'two saturable magnetic cores 63 and 64 having thereon reactance or power windings 65 and 66 respectively, D.C. control windings 67 and 68 respectively, and DC. bias windings 69 and 70, respectively. The power windings 65 and 66 'are each connected in a branch circuit with the branches being connected in parallel between VVcorrnnon junctions 7l and 72 of the two branches. The junction 7l is connected to an A.C- input terminal. 'I3 of a `full-wave bridge-type rectifier 74 while the junction 72 is connected to a terminal 75 which in turn connects with the conductor 55, Another A,C. input terminal 7670i the rectifier 74 is connected to a terminal 7d which in turn connects with the conductor 56. The terminals 75 and 78 form the A.C. power input terminals of the amplifier while the terminals 73 and ,'76 -form the A.C.. power voutput terminals of the amplifier as well as the A.C. input terminals of the rectier 7 4.

A one-way valve or half-wave rectifier di) is connected in series with the power winding 65 and a half-wave rectier 81 is connected in series with the power winding 66. The half-wave rectifier's 80 and S1 are oppositely related or poled with respect to a supply voltage applic, to the amplifier power input'terminals 75 and 78 so that the rectiiiers .conduct current ou Opposite .half cycles of the power supply voltage, and providey an A.C. output at the amplieroutput trminalsi and 76. Thus, half? andthe vdirection or sense of these M.M.F.s is referred to as the desaturation direction. The relative directions of the M.M.F.s resulting from current iiowing in the various bias and control windings are indicated by arrows adjacent these windings. y

"In general, in an arrangement employing two separate cores per amplifier, eachrcore carries one power winding and at least one control winding, while if the cores" are close together or if the well known single three-legged core is employed, a singlercontrol winding may'encircle' both cores or the center leg of the three-legged core. "in

any case, the induced alternating current voltages or the alternating fluxes due to the pulsating kcurrent through each power winding arev made vto cancel out with respect to the control windings and bias windings any are used.

The self-saturating amplifier 62 is similar to the amplifier 6 0 andv like parts vare identified by like numbers except that the numbers are primed. The A.C. power input terminals of both amplifiers are shown connected to the same power source, i.e., bothare connected to the conductors S'S-and 56 which in turn are connected across the output conductors 27 and 28 of the transformer 16.

The A.C. `,output current of the amplifier 6,0 is rectified by the'full-wave rectifier 74 with D.C` output terminals 83 and 84 of the rectifier being connected to supply D C. control currents to the reactor bridge control windings 36D'C and 40DC through an adjustable resistance 85. The A.C. output'l current of amplifier 6,2*is rectified by the full-wave rectifier 74 with D.C. output terminals 83 .and 84 of this rectifier connected to supply D.C. control currentsvtothe reactor bridge control windings MDC and 38DC through an adjustable resistance 85.

T he control windings 67, 63, 67 and 68 are connected in series and are connected to the D.C. output terminals of a Vfullwave rectifier 87 through anadjustable resistance 88. '.,lfhe A.C. input terminals Lofthe rectiler VS7 are connected to the output terminals 58 of the voltage detector 52.

The control windings 67 and 68 are wound and connected so that current flow through these windings results in desaturating M.M.F.s which tend to decrease the output of amplifier 60. The control windings 67' and 68, however, are wound and connected so that current flowing through them results in saturating M.M.F.s which tend to increase the output of amplifier 62. Thus, the control windings are energized in response to the output of the voltage detector, and, as indicated by the arrows adjacent the control windings of each amplifier, the current supplied by the detector 52 causes the output current of one of the amplifiers to increase while the output of the other tends to decrease for a given change in current supplied by the detector.

The bias windings ofv each of the amplifiers are connected to any suitable current source. As illustrated in the drawing, the bias windings 69 and 70 of amplifier 60 are connected to a battery 90 through an adjustable resistance 91. The direction of bias current is such that the M.M.F. produced thereby is in the saturating direction as indicated by the arrows adjacent the windings 69 and 70. The magnitude of the bias current is so adjusted that when a small or zero signal is applied to the control windings 67 and 68 the output of the amplifier 60 is high or at its maximum value. The bias windings 69' and 70 of amplifier 62 are shown connected to be supplied from a battery 90' through an adjustable resistance 91', and the direction of bias current in these windings is such that the M.M.F. produced is in the desaturating direction as indicated by thevarrows adjacent these windings. The magnitude of this bias current is so adjusted that when a small or zero signal is applied to the control windings 67 and 68' the output of amplifier 62 is low or at its minimum value.

The voltage detector 52 acts as a current regulating valve which does not permit an appreciable current to flow therethrough until the voltage applied to its input terminals 54 exceeds a predetermined critical value, and then the increase in current fiow to its output circuit is in direct proportion to the increase in voltage above that critical value.

It will be assumed herein for illustration only that the output voltage V2 is 'to be maintained within il% of the predetermined desired or normal value even though the supply voltage may vary from }-l()% to 10% of its normal value. Thus, in Fig. 2, there is shown a typical characteristic curve of the detector 52 in which the output current of the detector (going to the control coils 67, 68, 67' and 68') is along the abscissa axis and the output voltage V2, in percent of the normal value, is along the ordinate axis. There is also shown in parenthesis along the abscissa axis the corresponding supply voltage in percent of its normal value. It is seen from this curve that the detector has a low or negligible output current when the output voltage V2 is at its minimum permissible value (99% of the normal value) and that the output current increases rapidly and substantially in porportion with an increase in output voltage V2 above the minimum permissible value.

Any suitable voltage detector having a similar characteristic curve as that shown in Fig. 2 may be used. The detector 52, shown in Fig. l, is of a well known type which consists simply of a coil wound on a saturable core and designed such that the core tends to saturate at `a desired magnitude of voltage appliedl to it so that the current through the coil increases rapidly after saturation.

Referring to Fig. 3, the curve A represents the control characteristic of amplifier 60 (i.e., the output of' amplifier 60 to coils v36DC and 46DC, based on the current flowing from the detector 52) and the curve B represents the characteristic curve of amplifier `62 (i.e., theoutput of. amplifier 6 2 to coils 34DC and 38DC, based on the curent iiowing from the detector 52). It will be noted that for a negligible or zero control current applied to the control windings 67, 68, 68' and 67 by the detector 52, the output of amplifier 60 is at a high or maximum value such as indicated by a point a1, on curve A, while the output of amplifier 62 is at a minimum value, such as indicated by a point b1, on curve B. As the output current of the detector increases from the negligible value, the output of amplifier 60 (curve A) decreases from the maximum value (point a1) to a minimum value such as that at point a2, while the output current of amplifier 62 (curve B) increases from the minimum value (point b1) to a maximum value such as that at point b2. Thus, it is seen from Figs. 2 and 3 that the output of amplifier 62 is directly proportional to the magnitude of the output voltage above the minimum permissible value, while the output of amplifier 60 is inversely proportional to the magnitude of output voltage above the minimum permissible value.

The two characteristic curves A and B are shown on the same graph (Fig. 3) and cross at a point p" where the output current of each of the amplifiers is the same and at a relatively low value. The magnitude of the output of each amplifier being the same at point p, the

two pairs of diametrically opposite reactors of the bridgey 32 are equally energized and the bridge 32 is in balance. It will be apparent that the shape of the curves A and B and the location of the crossover point p" can be varied, as for example, by changing the ratio of the current in the bias windings 69 and 70 with respect to the current in the bias windings 69 and 70.

The operation of the complete voltage control device 10 is described in detail in the previously mentioned application Serial No. 497,978, and will only briefly be described herein.

When the output voltage V2 is at its normal value, no adjusting or compensating voltage e is required. Therefore, when the output voltage V2 is at 100% of its normal value (Fig. 2) the amplifiers 60 and 62 provide equal con,- trol currents (point p, Fig. 3) to the two pairs of diametrically opposite bridge reactors so that the bridge 32 is balanced. Thus, assuming that the voltage drops across the reactors in the bridge are equal and cophaseal (a condition which will be discussed more fully hereinafter) the voltage across bridge corners 44 and 48 will be relatively low and substantially ineffectual with regard to the magnitude of the ouput voltage V2.

If the supply voltage V1 increases above its normal value, the output voltage V2 tends to increase, causing an increase in the output current of the detector 52 which, in turn, increases the output current of amplifier 62 while tending to decrease the output current of amplifier 60,

as seen by the curves A and B in Fig. 3. The increase in output current of amplifier 62 tends to saturate the bridge reactors 34 and 38 yso that the impedance of windings 34AC and 38AC decreases, while the decrease in the output current of amplifier 60 tends to increase the impedance of reactor windings 36AC and 40AC. Thus,v

the bridge circuit 32 is unbalanced and an adjusting voltage e appears across the terminals 44 and 48 of the bridge. This adjusting voltage e is of such magnitude and relative polarity or phase 'angle with respect to V1 that it opposes or bucks V1, thereby reducing the primary or induced voltage E so as to compensate for the increase in V1 and to maintain the output voltage V2 substantially constant i.e., within its predetermined limits.

On the other hand, if the supply voltage V1 decreases below the normal value, the output voltage V2 tends to decrease, causing a decrease in the output of detector 52 which in turn causes an increase in the output of ampli- `fier 6G while causing a decrease in the output of amplifier 62. The i'ncrease'of output current of amplifier 60 tends to saturate the bridge reactors 36 and 40 and to reduce the impedance of windings 36AC and 40AC, while the decrease in output current of amplifier 62 tends conditions exist only rarely.

loaded, the voltage drops across the different reactors of the bridge circuit are not cophaseal due to load current tude and relative polarity or phase angle with respect;-

to V1 that it aids or boosts V1, thereby increasing the primary or induced voltage E so as to compensate for .the decrease in V1 and maintain the output voltage V3 substantially constant within its predetermined limits.

Up to this point it has been assumed that the vol-tage drops acrossthe bridge reactors are cophaseal in order to simplify the theoretical explanation of the control circuit 10. The cophaseal relationship between the voltage drops across the bridge reactors is very nearly obtained when the current flowing in the primary 22v of the transformer.

16 is small in comparison with the current flowing in the reactors of the bridge 32 due to the voltage across the corrector winding 30. However, these cophaseal voltage When the Vtransformer is owing through the bridge reactors, and the voltage relationsbecome much more complex. For example it has been found that under load conditions, vwhen the bridge is balanced, i.e., when equal currents ilow in the DC. conztrol winding of the bridge reactors, an undesirable voltage e appears'across the corners ist and 48 which Ais approximately at right angles to the voltage across corrector winding 38 andthe voltage E across the primary winding 22.

l' in such a case, tbe magnitude of the primary voltage E is close to its normal value and the magnitude of voltage V2 is close to its normal value regardless ofthe tact that 'the voltage e appears across the corners` 44 and 48 of the bridge. However, the primary voltage E, and there fore the voltageVz, is appreciably shifted in phase with respect to the supply voltage V1. It has also been found that. this undesirable voltage e contains relatively high harmonics which are transformed into the output voltage V2 and which may interfere with telephonic communications if the voltage control device is used to transmit power along lines which are close to telephone lines.

On the other hand, when the bridge circuit .32 is iun-` balanced, as for example when the ratio of the impedance values of the reactance winding 40AC tothe reactance winding 34AC and the ratio ofthe impedance values of the reactor winding 36AC to reactor winding 38AC are,

rather small, the voltage e acrossv the corners 44 and 48 attains a nearly cophaseal relationship with respect to the voltage across the corrector winding or corners 42 and 46, and also with respect to the primary voltage E. Consequently,y in such case the phase displacement vbetween V1 and V2 is small.` Also,-the magnitudes of the harmonics in the compensating voltage under unbalanced bridge conditions are'low. rihus, when the input voltage V1 and the output voitage V2 are normal, the bridge circuit is in balance andV n sa a voltage e exists across bridge corners 44'and 48 which is substantially at. right angles to the primary or induced.

voltage E., and which results in relativelyhigh harmonics in the output voltage Vzand an appreciable phase displacement between V1 and V2. Consequently, when the output voltage is normal'and a compensating voltage is notneeded but does exist, it is advantageous to reduce the magnitude ofthiscornpensating voltage e to a ruiniinum, and this is a'function of the present invention.

in the illustrated embodiment of the present invention, the undesirable compensating voltage e which appears across terminals te and 48 of the bridge when the output voltage V2 is normal, isA greatly reduced so as to reduce the harmonics in the output voltage to a minimum and also to greatly reduce the phase shiftbetween the supplf. voltage V1 and output voltage V2. This is accomplished by` connecting the variable impedance device 112, which is referred to asa harmonic and phasev shift suppressor,

across terminals 44 and 48 ofthe bridge circuit'32 and automatically varying the impedance of the device in response to variations in the controlled output voltage V2 in such a manner that when the output voltage V2 is nor-V mal, the impedance of the device is at a minimum, andy when the output voltage varies from normal, the impedance of the device is relatively high.

The phase shift and harmonic suppressor 12 shown in Fig. l comprises a saturable core reactor having a saturabie magnetic core 92 on which is positioned a reactance winding 94 and a DC. control winding 95. The reactance winding 94 has one end connected to the corner 44 and the other end connected to the corner 48 of the bridge circuit 32.

The suppressor control circuit 14 in Fig. `1 includes a self-saturating magnetic amplifier 96 which is somewhat similar to the amplifiers 60 and 62. Thek amplifier 96 is controlled in responseY to output voltage variations andv Y its output is supplied to the control winding 95 of thesuppressor reactor 12. I Y

The amplifier 96 includes two saturable magnetic cores 98 and 99 containing reactance or power windings 100 and 102, respectively, control windings 104 and 105,

respectively, control windings 106 and 107,'respectively,'

and Vvbias windings 108 and 109, respectively.

The power windings 100 and 102 are connected in a pair of parallel branch circuits 110 and 112, respectively, with the opposite ends of the branches having common junctions 114 and 11,5. A half-wave rectifier 116 is connected in branch 110 in series with the power winding 100, and a half-wave rectifier 117 is connectedin branchV 112 in Vseries with power winding 102. lThe junction .114 is y'connected to terminal v11,8 `of, a pair of amplifier A.C. output terminals 11S and 118", while the junction 115 is connected to terminal 120 ofn a pair of amplifier A-.CL`

power input terminals 120 and 120. The power input terminal 120 and the power output terminalll are connected together.

-The'power input terminals 1:20Vand 120 areconnected to an A.C. power source indicated by the numeral 122, while the A.C. output terminals 118 and 118' of the amplifier are connected to a full-wave rectifier 124 whose D.C. output terminals are connected to thecon- Y supply voltage and provide an alternating currentat out# put terminals 118 and 118. rillus, intermittent pulsating unid1rectional current flows in the power windings 100 and 102 and` produces saturating M.M.F.s which tend to saturate the cores and increase the output of the amplifiers. Thefdirection of these saturati'ng M.M.F.s are indicated by the arrowsV adjacent the power windings 100 and 102. j

The pair of rcontrol windings 104 and 105Y of amplifier 96 areconnected in s'eries`andvconnected by conductors 126and 127 through'an adjustable'resistance 128 f across the D C. output vterminals 83 andV 84 of the rectiI iier 74 and are therefore energized in response to the Y output of farnpliiier. 60. The pair of control windings 106 and 107 of the amplier 96, in likeV manner, are connected in seriesand connected by conductors 129 and 138 through an adjustable resistance 131V across the D C. outputV terminals 83. and 84 of the `rectier.74 and therefore are energized vin response to the output of Y amplifier 62. Thus, in the circuit of Fig. l, the outputs of amplifiers 60 and 62, control the relativerim-pedances of the reactors in the bridge 32 and. also determine the output of amplifier 96, which in turn controls the impedance of the suppressor reactor 12.

The bias windings 108 and 109 are shown connected in series and to a bias current source indicated as a battery 133 and a series adjustable resistance 134. As indicated by the arrows adjacent these bias windings, the M.M.F.s resulting from bias current flowing therethrough are in the saturating direction tending to raise the output of the amplifier. The magnitude of bias current for amplifier 96 is adjusted so that for a minimum total control current fiowing in the control windings 104, 106, 107 and 105, the output of the amplifier 96 is at its maximum value.

The control windings 104, 105, 106 and 107 are so connected and wound that the M.M.F.s resulting from current flow in these windings are in the desaturating direction as indicated by the arrows adjacent the windings, that is, these M.M.F.s oppose saturation and tend to decrease the output of the amplifier 96. Thus, the output currents from both of the amplifiers 60 and 62 affect the amplifier 96 in the same sense so that their combined effect may be represented by the curve C in Fig. 3. With the output current of each of the amplifiers 60 and 62 at a relatively low value at the crossover point p, the change in output current of one of the ampliers will be greater than the change in output current of the other for a given change in the output current of the detector. Curve C represents the control ampere-turns of amplifier 96 and is obtained by adding the instantaneous values of the curves A and B.

Fig. 4 shows the control characteristic curve D of the amplifier 96. A

Fig. 5 shows a curve Z which represents the impedance curve of the suppressor reactance winding 94 in relation to the control characteristic of the amplifier 96. It will be apparent that the output of the amplifier 96 (curve D) varies inversely with respect to the control ampereturns of the amplifier (curve C), i.e., the output of arnplifier 96 decreases as the ampere-turns increase, and vice versa. `It will also be noted from the curves D and Z (Figs. 4 and 5) that the impedance of the reactance winding 94 varies inversely with respect to the output of the amplifier 96.

In operation, when the output voltage V2 is normal, the detector 52 provides a control signal (indicated at a point n in Fig. 2) to the control windings of the amplifiers 60 and 62 which causes their respective outputs to be equal, as indicated at the cross-over point p in Fig. 3. This provides the two pairs of diametrically opposite control windings of the saturable reactor bridge circuit 32 with equal D C. control currents whereby the bridge circuit is balanced. At the same time, the control windings 104, 105, 106 and 107 of amplifier 96 are energized by a control signal of minimum value, as indicated at point m on curve C, so that amplifier 96 has a maximum output (indicated by point d1 on curve D, Fig. 4) to cause a relatively large current to fiow through the control winding 95 of the suppressor reactor and reduce the impedance of the A.C. reactance winding 94 to a minimum value, as indicated by the point 21 on curve Z in Fig. 5. Thus, when the output voltage V2 is normal, the bridge is balanced and the otherwise present undesirable voltage e, is made substantially ineffectual due to the fact that the suppressor reactor has a very low impedance and is connected across the bridge corners 44 and 48.

If the impedance ofthe suppressor reactance winding 94 could bev reduced to zero when the output voltage is at its normal value, there would (in effect) be a short circuit across the diametrically opposite corners 44 and 48 of the bridge, and this would reduce the adjusting voltage e to zero, and there would be no high harmonics in the output voltage nor pbase displacement whatsoever between the supply voltage and output voltage as a result of the control system. With the present inven- 0n the other hand, if the output voltage V2 tends to vary above or below the normal value, the amplifier 96 automatically causes the impedance of reactance winding 94 to increase so that the compensating voltage e is effective in holding the output voltage V2 within its predetermined limits.

Thus, for example, if the output voltage V2 tends to increase above its normal value due to the supply voltage V1 increasing to 110% of its normal value, the small increase in output voltage causes the output of the detector 52 to increase to a high value indicated at point h on the curve in Fig. 2, thereby increasing the ouput of amplifier 62 to a relatively high value (point b2, curve B) while decreasing the output of amplifier 60 to a low value, (point a2, curve A). This causes the saturable core reactor bridge 32 to become unbalanced and produce a correcting voltage e which opposes the irnpressed voltage V1 so as to maintain the primary or induced voltage E substantially constant. At the same time, the resultant effective desaturating control M.M.F.s due to signal currents from the amplifiers 60 and 62, which are applied to the control windings of amplifier 96, are increased to a high value, as indicated by point c1 on curve C, and the output of amplifier 96 is decreased to a low value, as indicated at point d2 on curve D, Fig. 4; consequently, the impedance of suppressor reactance winding 94 is high, as indicated by the point z2 on curve Z in Fig. 5. Because the impedance of winding 94 is high, it has substantially no effect on the voltage e developed in the bridge. Therefore, the

Voltage e is effective and opposes the supply voltage V1, thereby tending to reduce the primary or inducedl voltage E and maintain the voutput voltage V2 within its predetermined limits.

In like manner, if the output voltage V2 tends to decrease from the normal value, for example due to the supply voltage decreasing to of its normal value, the small decrease in output voltage causes the output cur rent of detector 52 to decrease to a low value, such as indicated at point l on the curve in Fig. 2. The decrease in output current of the detector 52 causes the output of amplifier 60 to increase (point a1, curve A) and the output of amplifier 62 to decrease (point b1, curve B) thereby producing control signals which cause the bridge circuit 32 to become unbalanced. At the same time, the desaturating control M.M.F.s due to signal currents from the amplifiers 60 and 62, which are applied to the control windings of the amplifier 96, are at a high value as indicated by a point c2 on curve C. Consequently, the out of amplifier 96 is again reduced to a low value as indicated at point d2 on curve D, Fig. 4, thereby causing the impedance of the suppressor reactor winding 94 to be high as indicated at point z2 on curve Z. Because of the high impedance of the winding 94 under this unbalancedbridge condition, the voltage e developed in the bridge 32 is again effective; however, in this case it is aiding the supply voltage V1 and tending to raise the primary or induced voltage E and to thereby maintain the output voltage V2 within its predetermined limn its.

Fig. 6 graphically illustrates the operation of the systern of Fig. 1 and the effect of the suppressor 12 and control circuit 14 in greatly reducing and maintaining the phase shift between V1 and V2 at a minimum. In Fig. 6 it is assumed that the output voltage V2 tends to vary due to variations in the supply voltage V1. The vector o-a represents the supply voltage at its normal value, the vector of-b represents the supply voltage when above normal, and the vector o-c represents the supply voltage when below normal. The dashed-line curve r represents the locus of thecndsof the compensating voltage ir vectors which would result it the automatic suppressor were not employed. The curve "s represents the locus of the ends of the compensating voltage vectors when the automatic suppressor is employed.

When V1 is above normal as indicated by vector o-b, the bridge 32 is unbalanced in the manner described above and the compensating voltage e, appearing across bridge terminals 44 and 48, is indicated by vector o-b. Combining these vectors results in the vector E which represents the desired or normal primary or induced voltage necessary to obtain normal output voltage. When V2. is below normal as indicated by vector o-c, the bridge is unbalanced in the opposite sense and the compensating voltage e is indicated by the vector o--c. Combining vectors o-c and o-c results again in the vector E. Thus, if the supply voltage varies above or below its normal value, the compensating voltage e correspondingly affects the primary voltage in a manner tol maintain the output voltage at substantially its normal value. i y

The vector o--a" represents the voltage which would appear across the bridge terminals 44 and 48 when the supply and output voltages are substantially normal and the bridge is balanced, if the automatic suppressor were not employed. The vector o-a is substantially at right angles to V1 and vis of such magnitude that when combined with the normal supply voltage vector o-a, the primary voltage vector En is obtained. It is apparent that the phase shift between En and V1 is rather large and this would mean that the phase shift V1 and V2 would also be Vrather large.

The vector o--a' represents the reduced voltage which appears across the bridge terminals 44 and 4S-wh`en the output voltage V2 isnormal and the automatic suppressor of the present invention is employed. Y Combining the normal supply voltage vector o-a and the vector o-a' results in the desired primary voltage vector E. Thus it is apparent that when the output voltage V2 is at the desired value, the phase shift between the supply and outputvoltages is Vreduced and maintained substantially constant.

It was also found thatthe V.A.R. s (volt-ampere-reactive) required by the control system using the controlled suppressor reactor (for most load conditions) wasV less than that required when the suppressor reactor was not used.

Fig'. 7 shows a partial schematic diagram illustrating a modified form of the present invention, where, as in the circuit of. Fig. l, the suppressor reactor 12 is controlled in response to variations in the output voltage V2. However, in the circuit shown in Fig. 7, the suppressor control amplifier 96a has only one pair of control windings 136 and 133 and these control windings are supplied by the direct current output of a full-wave rectifier 14).

YThe rectifier 140 has its alternating current input terminais connected to be supplied by a voltage' proportional to the difference between theAC. output voltages of the amplifiers 60 and 62.

Thus, rectifier 14S has Vone ofv its A.C. input terminals connected to the AJC. output terminal 73 of the amplifier 60 by .a conductor 142, while the other input terminal of the rectifier is connected to the A.C. output terminal. 73 of the amplifier 62 through a conductor 3144. Therefore, as in the circuit of Fig. l, the outputs of the amplifiers 60 and 62 control the impedance of the reactorl 12.

The amplifier 96a, like amplifier 960i Fig. 1, is shown y the-rectifier 140 will vary from zero to arelatively high value in accordance with the difference between the A C. outputs of the amplifiers 60 and 62.

When the output voltage V2 is at its normalvalue, the amplifiers 60 and 62 have substantially equal output currents and operate to balance the bridge 32. Therefore, the potential between terminals 73 and '78 is substantially equal to the potential between terminals 73' and 78 since both amplifiers are supplyingV substantially equalcurrents to substantially equal loads; the loads here being the D.C. control circuits ofthe bridge 32. Thus, the voltage across'the terminals 73 and 73', and therefore across the A.C. input terminals of the full-wave rectifier 140, is substantially zero. It will be evident therefore, that Ywhen the output Voltage V2 is normal andthe bridge is balanced, the control' windings 136 and 138 have little or no current flowing through them and the output of amplifier 96a is at its maximum value, thereby causing the impedance of the suppressor reactance winding 94 to be at its minimum value as desired. If the output voltage V2 drops to a value below normal, as for example due to the supply voltage decreasing to 90% ofits normal value, the output of amplifier 60 increases while the output of amplifier 62 decreases. Because the change in output current of amplifier 60 (curve A, Fig. 3) is greater than the change in lthe output current of amplifier 62 (curve B, Fig. 3) the terminals 73 and 73' wil1 be at different potentials and an A.C. voltage Y will exist across the conductors 142 and 144. Control y and 1,38 thereby producingdesaturating control M.M. F.s

source 133', 134". The biascurrent flows inthe saturating direction through the bias windings 10S'V and 1091 Vand the-magnitude of bias current is adjusted so that a high current flows in -the Voutput circuit of theV amplifier 96a when a low or 'zero signal current'liows in the control windings 136 and 138. f

The signalY voltage applied. to the input terminals of to lower the output of amplifier 96a and cause the impedance of the A.C. reactance winding 94 to be increased.

Ifthe output voltage V2 increases to a value above normal, as for example due to the supply voltage increasing to of its ,normal value, the output of amplifier 62 increases ywhile the output of amplifier 60 decreases. Because the change in the output' of ampli- 'fier 62 is greater than the change in the output of amplifier 60 (curves A and B, Fig.r3), the potentials of the terminals 73 and 73 are different, and an A.C. voltage exists Vacross the conductors 142'andV 144, thereby producina desaturatng M.M.F..s and reducing the output of amplifier'96a and causing the impedance of the reactance winding `94 to be high.

Thus, the suppressor reactor-12 in Fig. 7 is also automatically controlled in response to variations in the output voltage-V2 in suchmanner that the suppressor reactance winding 94 presents a minimum impedance across the bridge terminals 44 and 48 when the output voltage is normal, and a relatively high impedance across these bridge terminals when the output voltage tends tol vary from the normall value. v

The voltage impressed across bridge corners 42 and 46 in Fig. l is obtained byV means of' the corrector winding 30 on the transformer V16, however, this voltage may be obtainedvby means of a separate transformer. For

example, where it is desired to Vconnect a power supply sourcedirectly toa load circuit without the use of a powerV transformer, such as transformer 16, 'the voltage impressed across these bridge corners may be Yobtained from a separate transformer connected across the load circuit. Y

While the bridge circuit V32 in Fig. l is shownV connected` in power line 23 in series with the primary winding of power transformer 16, it V'may be` connected in the secondary winding side of the transformer if desired. Also, although the'bridge circuittispshowh conductively coupled 'into the power line, it may be coupled into a power line by means of an additional transformer. in such a case, instead of connecting the bridge corners 44 and '4d directly into the power line as shown, the primary. winding of the additional transformer is connected across 13 these bridge corners with the secondary winding connected in series in the power line.

It is to be understood that the foregoing description and the accompanying drawings have been given only by way of illustration and example, and that changes and alterations in the present disclosure, which will be readily apparent to one skilled in the art, are contemplated as within the scope of the present invention which is limited only by the claims which follow.

What is claimed is:

1. In a voltage control system comprising a Wheatstone type bridge circuit including two sets of opposed impedances and two sets of opposed corners, means for impressing a voltage across one set of corners, and means for varying the magnitude of at least one set of impedances responsive to a selected electrical condition in the system for producing a variable voltage across the other set of corners: the improvement which comprises a variable impedance connected between said other set of corners; circuit means for producing a signal responsive to said electrical condition; and means responsive to said signal for varying the magnitude of said impedance responsive to said selected electrical condition in the system.

2. In a voltage control system comprising a Wheatstone type bridge circuit containing two sets of opposed impedances and two sets of opposed corners, means for impressing a voltage across one set of corners, and means for varying the magnitude of at least one set of irnpedances for producing a variable voltage across the other set of corners, said means being responsive to a selected electrical condition in the system which varies from a normal value to values above and below normal: the improvement which comprises a variable impedance connected between said other set of corners; circuit means for deriving a signal responsive to the variations in said electrical condition; and means responsive to said signal for varying the magnitude of said impedance responsive to said selected electrical condition in the system so that the magnitude of the impedance is at a minimum when said electrical condition is at its normal value.

3. In a voltage control system containing power input and output circuits; means for producing a correcting voltage, including a Wheatstone type bridge circuit containing two sets of opposed impedances and two sets of opposed corners, and means for impressing a voltage across one set of corners, the other set of corners being connected in a circuit between the power input and output circuits; and means for varying the magnitude of both sets of impedances responsive to a selected electrical condition in the system, including a first and a second source of current: the improvement which comprises a variable impedance connected between said other set of corners; and means for varying the magnitude of said impedance responsive to the sum of the currents flowing from said rst and second sources.

. 4. In a voltage control system containing power input and output circuits; means for producing a correcting voltage, including a Wheatstone type bridge circuit containing two sets of opposed impedances and two sets ol opposed corners, and means for impressing a voltage across one set of corners, the other set of corners being connected in a circuit between the power input and output circuits; and means for varying the magnitude of both sets of impedances responsive to a selected electrical condition in the system, including a rst an-d a second source of electrical potential: the improvement which comprises a variable impedance connected between said other set of corners; and means for varying the magnitude of said impedance responsive to the difference between said tirst and second sources of electrical potential.

5. In combination in a voltage control system, power input and output circuits; means for producing a correcting voltage, including a Wheatstone type bridge circuit containing two sets of saturable core reactors and two sets of opposed corners, and means for impressing a voltage across one set of corners, the other set of corners being connected in a circuit in series between the power input and output circuits; means for varying the impedances of the saturable core reactors responsive to a selected electrical condition in the system, including a rst source of D.C. current connected to one set of reactors and a second source of D.C. current connected to the other set of reactors; a variable impedance connected between said other set of corners; and means for varying the magnitude of said impedance responsive to the sum of the D.C. currents owing from said rst and second sources of D.C. current.

6. In an electrical control system containing power input and output circuits; means for producing a correcting voltage, including a Wheatstone type bridge circuit having two sets of opposed impedances and two sets of opposed corners, and means for impressing a. voltage across one set of corners, the other set of corners being connected in a circuit between the power input and output circuits; and means for varying the magnitude of at least one set of impedances: the improvement 'which comprises a saturable core reactor connected in circuit between said other set of corners, means for producing a current directly proportional to said electrical condition above a predetermined magnitude, means for producing a current inversely proportional to said electrical condition above said predetermined magnitude, and means responsive to said currents for reducing the impedance of said reactor to a minimum only when said currents are substantially equal.

7. In an electrical control system having means for producing a variable voltage across a pair of circuit terminals, said means including two sets of saturable core reactors, means responsive to an electrical condition in the system for varying the impedance of at least one set of reactors when the magnitude of said electrical condition varies from a predetermined value; the improvement which comprises an additional saturable core reactor connected in circuit across said circuit terminals, means for varying the impedance of said additional reactor and other means connected to said impedance varying means and responsive to said electrical condition, said other means changing the current How through the impedance varying means to reduce the impedance of said last named reactor to a minimum only when the magnitude lof said electrical condition is at said predetermined value.

`8. In combination in a voltage control system, a power input circuit connectable to a supply voltage source; a power output circuit connectable to a load; means for producing a correcting voltage, including a Wheatstone type bridge circuit containing two sets of saturable core reactors and two sets of opposed corners, and means for impressing a voltage across one set of corners, the other set of corners being connected in a circuit in series between the power input and output circuits; means for varying the impedances of the saturable core reactors responsive to a selected electrical condition in the system, including a first source of D.C. current connected to one set of reactors and a second source of D.C. current connected to the other set of reactors; a variable impedance connected between said other set of corners; and means for varying the magnitude of said impedance responsive to the sum of the D.C. currents owing from said rst and second sources of D.C. current, including a magnetic amplifier containing two control windings, one of said control windings being connected to the first source of D.C. current, and the other of said control windings being connected to the second source of DC. current.

9. In combination in a voltage control circuit, a power input circuit connectable to a supply voltage source; a power output circuit connectable to a load; means for producing a correcting voltage, including a Wheatstone,

c type bridge circuit containing two sets of saturable core reactors and two sets of opposed corners, and means `for impressing a voltage across one set of corners, lthe other set of corners being connected in a circuit in series between the power input and output circuits; means for varying the impedances of the saturable core reactors responsive to a selected electrical condition in the systern, including a iirst source of D.C. current connected to one set of reactors and a second source of D.C. cur rent connected to the other set of reactors; a saturable core reactor connected between said other set of corners; a self-saturating magnetic amplier containing apower winding and two control windings, the control windings 'being wound so as to oppose the M.M.F. of the power winding; connections between the first source of DC. current and one of said control windings; connections between the second source of D C. current and the other of said control windings; and means connecting the output ot the amplier with the saturable core reactor connected between said other set of corners so that the impedance of said last named reactor varies inverselyr with the output of the amplifier.

10. In combination in a voltage regulating circuit, a transformer containing a main primary winding and a main secondary winding; means connected with one of said windings for producing a correcting voltage, including a Wheatstone type bridge circuit containing two sets Yof saturable core reactors and two sets of opposed corners, and transformer means for impressing a voltage across one set of corners,rthe other set of corners being connected in the circuit containing said'one of said main windings; means for` varying the impedances of the saturable core reactors responsive to ya selected electrical condition in the circuit, including a rst source of DC. current connected to one setV of reactors and a second source of DLC. current connected to the other set ol= reactors; a saturable core reactor connected between said other set of corners; a self-saturating magnetic amplitier containing a power winding, two control windings, and a bias winding; the control windings being wound so as to oppose the M.M.F of the power winding, and the biasrwinding being wound to aid the M.M.F. of the power winding; a source of bias current connected to the bias'winding; means for varying the current through the bias winding; connections between the` rst source out D C. current and one of said control windings; connections between the second source of D.C. current and the other of said control windings; and means connect` ing the output Vof the amplifier with the saturable core reactor connected between said other set of corners' so that the impedance of said last named reactor varies in-` versely with the output of the amplifier.

l1. in combination in a voltage regulating circuit, a transformer containing a main primary winding and a main secondary winding; means connected with one of said main windings for producing a correcting voltage, including a Wheatstone type bridge circuit containing two sets of saturable core reactors and two sets of opposed corners, and a corrector winding connected to supply a voltage across one set of corners, the other set of corners being connected in the circuit containing said one of said main windings; means for varying the impedances of the saturable core reactors responsive to a selected electrical condition in the circuit, including a first source of D.C. current connected to one set of reactors and a second source of D.C current connected to the other setof reactors, whereby there is a potential drop across eac'h'set of reactors; a' variable impedance connected the magnitude of said variable impedance responsive to the difference in the potentials across the two sets ofreactors, including a self-saturating-magnetic amplifierl containing two power windings, and a control winding wound to oppose the MMF. of the power windings, the control-winding being connected tothe D;C.` current sourcesL 16 l so that the current which ows through said con rl winding is proportional to said diterence in potential across the two sets of reactors.

l2. in combination, two sets of opposed saturable cor' reactors, each set including two A.C. reactance windings and at least one D.C. control winding, the A.C. reactance windings of the sets being connected together to form a Wheatstone type bridge circuit having two 4sets of diametrically opposite bridge corners, means for im pressing an A.C. voltage across one set of bridge corners, means for controlling the balance conditions of said bridge circuit including said D.C. control windings, a saturable core reactor including a reactance winding. connected in circuit across the other set of bridge corners, means for varying the impedance of said last named reactor, and other means connected to the impedance varying means and responsive to the balance conditions of said bridge circuit for changing the current flow through said impedance varying means so asV to reduce the impedance of said latter reactance winding to a minimum only when said bridge circuit is in balance.

13. In an electrical control system containing means for producing a variable voltage, said means comprising at least four impedances connected together to form a Wheatstone type bridge circuit having two sets of opposed bridge corners, means for impressing a voltage across ono set of bridge corners, and means for varying the value of at least one of said impedances for produccorners; the combination with the voltage producing' means of a shunt circuit connected across said other set` of bridge corners, a variable impedance device connected in said shunt circuit, means for varying the impedance of said device, and other means connected to said impedance varying means responsive to the magnitude of an electrical condition of the system changing the current ow through the impedance varying means so as to reduce the impedance of said impedance device to a minimum when the magnitude of said'electrical condition is at a predetermined value, and for increasing the impedance oi said device when said electricalV condition varies from said predetermined value. Y

14. in an electrical control system containing means fo; producing a variable voltage, said means comprising' at least four impedances connected together to form a Wlieatstonetype bridge circuit having two sets of opposed bridge corners, means for impressing a voltage across one set of bridge corners, and means for varying the value of at least one of said impedances for producing said variable voltage across the other set of bridge corners; the combination with the voltage producing means of a shunt circuit connected across said other set of bridge corners and including a saturable reactor containing a magnetic core, an A.C. reactance winding onL said core, and a D.C. control winding on said core for controlling the impedanceof said reactance'winding, an amplifier having' an output circuit connected to supply output current tosaid control winding, and a signal input circuit for controlling the magnitude of said output cur-4 rent, and means for energizing said signal input circuitk in response to the magnitude of an electrical conditiony ot the system to increase the magnitudefof said output current to a maximum when said electrical condition is at a predetermined magnitude and to decrease said output current when said electrical condition varies ,from-said; predetermined magnitude.

l5. in an electrical control system containing means for producing a variable voltage, said means comprising at least four impedances connected together to formY al Wheatstone type bridge'circuit having two sets of.op-

posed bridge corners, means for impressing a voltage' across one set of bridge corners, and means for varying the value of at least one of said impedances for producing said variable voltage across the othery set of bridge corners; the combination with the voltage pro- .17 ducing means of a shunt circuit connected across .said other set of bridge corners and including a saturable reactor containing a'magnetic core, a reactance winding on said core, and a control winding on said core for controlling the impedance of said reactance winding, means for producing a first signal directly proportional to an electrical condition of the system above a predetermined magnitude, means for producing a second signal inversely proportional to said electrical condition above said predetermined magnitude, means for combining said first and second signals to produce a third signal, and means responsive to said third signal for energizing said control winding.

16. An electric control system comprising a power input circuit connectable to a supply voltage source, a power output circuit connectable to a load, means including a pair of conductors for connecting the power input circuit with the power output circuit, a bridge circuit including four impedances connected together to form two sets of opposed'impedances and two sets to diametrically opposite bridge corners, means for impressing a voltage across one set of corners, means for varying at least one of said impedances to provide a variable voltage across the other set of corners, means coupling said variable voltage in series with said supply voltage, a shunt circuit connected across said other set of corners, a saturable reactor including a magnetic core', a reactance winding on'said-coreand connected in said shunt circuit, and a control winding on said core, first and second amplifiers, means for controlling the output of each of said amplifiers in response to an electrical condition of the system, said first amplifier producing an output which decreases when said electrical condition increases above a predetermined magnitude, said second amplifier producing an output which increases when said electrical condition increases above said predetermined magnitude, a thirdamplifier having an output circuit connected to supply output current to said reactor control'winding, and means for controlling the output current of said third amplifier in response to the outputs of said first and second amplifiers.

f7. An electrical control system comprising a system power input circuit connectable to a supply source, a system power output circuit connectable to a load, a bridge circuit including four saturable core reactors connected together to form two sets of diametrically opposite reactors and two sets of diametrically opposite bridge corners, each set of reactors having at least one D.C. control winding, means for impressing a voltage across one set of bridge corners, means including the other set of corners for connecting said bridge circuit in series between the power input and output circuits, a shunt circuit connected across said other set of bridge corners, a saturable reactor including a magnetic core, a reactance winding on said core and connected in said shunt circuit, and a reactor control winding on said core, a pair of self-saturating magnetic amplifiers, each of said amplifiers comprising power input and output circuits, a saturable core, a power winding on said core and connected between the power input and output circuits, and a control winding on said core, means for producing a signal responsive to an electrical condition of the system, means for supplying said signal to the control winding of each of said amplifiers for inversely affecting the outputs of said amplifiers, means for energizing one D.C. control Winding in response to the output of one of said amp'ifiers, means for energizing the other D.C. control winding in response to the output of the other of said amplifiers, a third amplifier comprising power input and output circuits, a saturable core, a power winding on said core and connected between the power input and output circuits, and a signal input circuit including a control winding on said core, means for energizing said signal input circuit of said third amplifier in response to the outputs of said pair of amplifiers, and means for ener- ,1.8 gizing said reactor control winding of the reactor of saidl shunt circuit in response to the output of said third amplifier.

18. An electric control system comprising a system power input circuit connectable to a supply source, a system power output circuit connectable to a load, a bridge circuit including four saturable core reactors con'-4 nected together to form two sets of diametrically oppof site reactors and two sets of diametrically opposite bridge corners, each set of reactors having at least one D.C, control winding, means for impressing a voltage across one set of bridge corners, means including the other set of corners for connecting said bridge circuit in series between said power input and output circuits, a shunt circuit connected across said other set of bridge corners, a saturable reactor including a magnetic core, a reactance winding on said core and connected in said shunt circuit, and a reactor control winding on said core, a pair of self-saturating magnetic amplifiers, each of said am-l plifiers comprising power input and output circuits, a saturable core, a power winding on said core and connected between the power input and output circuits, a rectifier in series with the power winding for producing self-saturating M.M.F.s when a voltage is applied to the power input circuit, and a control winding on said core, means for producing a signal responsive to the voltage across said system output circuit, means for energizing the control winding of one of said amplifiers in response to said signal to produce desaturating M.M.F.s, meansl for energizing the control winding of the other amplifier in response to said signal to produce saturating M.M.F.s, means for energizing one D.C. control winding in response to the output of one of said amplifiers, means for energizing the other D.C. control winding in response to the output of the other of said amplifiers, a third amplifier comprising power input and output circuits, a saturable core, a power winding on saidy core and connected between the power input and output circuits of the third amplifier, a rectifier in series with the power winding for providing self-saturating M.M.F.s when a voltage is applied to the power input circuit of the third amplifier, and a signal input circuit including at least two control windings on said core, means for energizing one of said latter control windings in response to the output of one of the amplifiers of said pair, means for energizing the other of said latter control windings in response to the output of the other amplifier of said pair, and means for energizing said reactor control wind'- ing of the reactor in said shunt circuit in response to the output of said third amplifier.

19. In an electrical control system having an A.C. source, means for producing a variable phase voltage across circuit points in the system, including means for varying the phase of said voltage with respect to the voltage of said source in response to an electrical condition in the system which varies from a normal value to values above and below normal, the improvement which comprises impedance means connected between said circuit points, circuit means for deriving a signal responsive to said electrical condition, and means including impedance control means responsive to said signal for reducing the value of said impedance means to a minimum when the electrical condition is at its normal value and increasing the value of said impedance means when the electrical condition varies above or below the normal value.

20. The combination of a bridge circuit having bridge input and output circuits, means for supplying a voltage to the bridge input circuit, bridge control means for controlling the balance of the bridge circuit to provide a variable voltage at the bridge output circuit; and a variable impedance device connected in a circuit across the bridge output circuit, said variable impedance device comprising a variable impedance member, means for varying the impedance of said member, circuit means connected to said impedance varying means for producing a signal responsive to the balance conditions of the bridge circuit, said circuit means including means responsive to said signal for changing the current flow through the impedance varying means so as to vary the impedance of the impedance member in such a way that the impedance is at a relatively low value when the bridge is balanced and at a higher value when the bridge is unbalanced.

2l. The combination of a bridge circuit having bridge input and output circuits, means for supplying a voltage to the bridge input circuit, bridge control means for con trolling the balance of the bridge circuit to provide a variable voltage at the bridge output circuit, a variable impedance device connected iu a circuit in parallel with the bridge output circuit, and means for varying the impedance of said device so that it is at a minimum when the bridge is substantially balanced and at a higher value when the bridge is unbalanced, said latter means cornprising an amplifier having an output circuit and a sig nal input circuit for controlling the outputrof the ampliier, circuit means for energizing said signal input circuit in response to the balance conditions of the bridge circuit, and means for varying the impedance of said device in response to the output of said amplifier.

22. In an electrical control system including a transformer having a main winding for supplying power to a power output circuit, a bridge circuit having bridge input and output circuits, means for supplying a voltage t the bridge input circuit, bridge control means for controlling the balance of the bridge circuit in response to an electrical condition of the system which is variable from a normal value to values above and below the normal value, means coupling the bridge output circuit in series with said main winding, a variable impedance device connected in a circuit across the bridge output circuit, circuit means responsive to said electrical condition for producing a signal which varies from a minimum value when said electrical condition is at said normal value to a higher value when said electrical condition varies above or below said normal value, an amplifier having an output circuit and a signal input circuit adapted to control the output of said amplifier, means for energizing said signal input circuit in response to said signal, and means for varying the impedance of said device in response to the output of said amplifier.

23. In an electrical power system including power leads for transmitting A.C. power from an A.C. power source to an A.C. power output circuit, the combination of a bridge circuit having bridge input and output circuits and including at least two saturable reactors each having an A.C. reactance winding connected in a different arm of the bridge circuit, each of said reactors having a D.C. control winding,kmeans coupling said bridge output circuit in series in one of said power leads, means for supplying an A.C. voltage to said bridge input circuit, control means including means for supplying D.C. current to the D.C. control windings of said reactors to control the balance of the bridge circuit for providing an` adjusting voltage at the bridge output circuit, an additional saturable reactor having an A.C. reactance winding and a D C.Y control winding, said latter A.C. reactance winding being connected in a circuit in parallel with said bridge output circuit, circuit means including a magnetic amplifier for deriving a signal responsive to the balance condition of the bridge circuit, and means for energizing the D.C. control windingA of said additional reactor in response to said signal.

24. ln an electrical control system, the combination of a bridge circuit having bridge input and output circuits and including at least two saturable reactors each having a reactance winding connected in a different arm of the bridge circuit, each of said reactors having a control winding, a pair of amplifiers each having an output circuit and a signal input circuit for controlling the output of the amplifier, detector means for deriving a signal responsive to an electrical condition in the system, means for energizing the signal input. circuits of said amplifiers in response to said signal for varying the outputs of said amplifiers inversely with respect to each other, means for supplying current variablein accordance with the output of one of said amplifiers to the control winding of one of said reactors, means for supplying current variable in accordance with the output of the other of said amplifiers to the control winding of the other of said reactors, an additional saturable reactor having a 'reactance winding and a control winding, said latter reactance winding being connected in a circuit in parallel with said bridge output circuit, a thirdV amplifier having an output circuit and a signal input circuit for controlling the output of said third amplifier, means for energizing said signal input circuit of the third ampliiier in response to the outputs of said pair of amplifiers, and means for energizing the control winding of said additional reactor in response to the output of said third amplifier.

References Cited in the file of this patent UNITED STATES PATENTS 2,657,352 Sink Oct. 27, 1953 

